(1) Field of the Invention
The present invention relates generally to abrasives and abrasive tools suitable for the grinding and polishing of various materials. This invention more particularly relates to porous, bonded abrasive articles impregnated with grinding aids and methods for making same.
(2) Background Information
The use of porous abrasive products to improve mechanical grinding processes is well known. Many high performance abrasive products require a controlled amount of porosity, and interconnected porosity, to be engineered into the structure of vitrified and resin bonded grinding wheels. Other abrasive products inherently include some amount of porosity. Pores typically provide access to grinding fluids, such as coolants and lubricants, which promote efficient cutting, minimize metallurgical damage (e.g., surface burn), and maximize tool life. Pores also facilitate the clearance of material (e.g., chips or swarf) removed from an object being ground, which is important especially when the object being ground is relatively soft or when surface finish requirements are demanding.
In certain grinding operations as defined by material being ground or mode of grinding, the inclusion of a grinding aid or treatment in a bonded abrasive product can be very beneficial. The aid or treatment can provide a variety of improvements to the grinding process including lubrication, cooling, prevention of loading (attachment of work material chips to the abrasive product) and reaction with the work material rendering it “easier-to-grind” via changes in hardness, ductility and phase. The result can be improved material removal efficiency and/or improved abrasive product life.
Conventional means to add grinding aids or treatments to bonded abrasive products depends on the type of bonding of the products. Products made with resin-type bonds can incorporate many types of grinding aids during the raw batching or mixing process. Subsequent curing of the products is done at relatively low temperature (room temperature through approximately 200° C.) and therefore does not thermally decay or decompose most grinding aids. The grinding aid or treatment remains in the product and can be utilized in a grinding or polishing process.
Various techniques have been and are used to fabricate porous bonded abrasive articles. All vitrified or glass bonded abrasive tools undergo high temperature treatment to form the glass bond and to bind the abrasive particles together. Any grinding aid incorporated into a vitrified product before firing would be thermally decayed or consumed during such a treatment. Therefore, any addition of a grinding aid to a vitrified product can only be feasibly added after the heating process.
Conventional means to add grinding aids or treatments to vitrified or glass bonded abrasive products involves impregnation of molten materials through dipping (Darcy's Law), pressure assist or vacuum assist techniques. These techniques offer disadvantages including variability in completeness and uniformity of impregnation and hazard potential. Handling of molten materials requires added safety procedures and typical grinding aids or treatments, such as waxes and sulfur, are flammable.
U.S. patent application Ser. No. 10/291,976 (the '976 application), entitled Supercritical Fluid (SCF) Extraction Method, filed Nov. 12, 2002, utilizes supercritical fluid processing as a method for extracting pore inducers from highly porous abrasive products. The '976 application is hereby fully incorporated herein by reference.
As market demand has grown for precision components in products such as engines, bearings, and electronic devices (e.g., silicon and silicon carbide wafers, magnetic heads, and display windows) the need has grown for abrasive tools for fine precision grinding of a range of relatively hard and/or brittle materials and soft, heat-sensitive materials. Therefore, there exists a need for further improving porous abrasive articles and tools.